Development of a Definition of Plastic Concrete for Cutoff Walls

ABSTRACT ONLY - Currently, the ICOLD Embankment Dams Committee is updating ICOLD Bulletin No. 51 – “Filling Materials for Watertight Cutoff Walls” first published in 1985. Plastic concrete is a term that has been used to describe various mixtures of cement, bentonite, aggregates, water, and various additives. Various forms of plastic concrete have been used in dam and levee construction; predominantly in foundation treatments and seepage barriers (cutoff walls). The intent of adding bentonite to the concrete mix is to increase the ductility and reduce the stiffness of the product to match the properties of the surrounding soil and/or rock. However, in addition to the changes in ductility and elasticity, the addition of bentonite has been observed to reduce the strength of mix and may also reduce the mix’s resistance to internal erosion. Furthermore, while the term “plastic concrete” has been used extensively in the past to describe material used in dam and levee construction, there does not appear to be a consistent definition of what the properties of these materials are expected to be. Also, there does not appear to be a recognized standard testing procedure to measure and evaluate the properties of plastic concrete that are pertinent to dam and levee construction and performance. Based on the 1991 Kahl et. al study, the U.S. Army Corps of Engineers (USACE) developed a design procedure for designing a workable (8-inch slump) mix to produce plastic concrete targeting values of compressive strength and unconfined elastic modulus. Deformation due to hydraulic loading, changes in the seepage regime, and modifications to the embankment can result in lateral movements within the embankment. It is the goal of the ICOLD Committee updating Bulletin 51 to put forth a “definition” for plastic concrete for the geotechnical engineering profession.